Process for regenerating a monofunctional large-pore zeolite catalyst having high selectivity for paraffin dehydrocyclization

ABSTRACT

The present invention is a process for regenerating a large-pore zeolitic catalyst that has been deactivated by the formation of Group VIII metal agglomerates on the catalyst surface. In the process, the Group VIII metal agglomerates are redispersed to produce agglomerates of small size. It comprises an oxychlorination step, a nitrogen purge step and a reduction step.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 944,403,filed Dec. 19, 1986, now abandoned and which is hereby incorporated byreference in its entirety.

FIELD OF INVENTION

The present invention relates to regenerating contaminated catalysts.More specifically, this application is directed to regeneratinglarge-pore zeolite catalysts.

BACKGROUND OF THE INVENTION

The invention described below relates to a process for regeneratinglarge-pore zeolite catalysts having a Group VIII metal which are used toreform petroleum feedstocks. Within the past few years such catalystshave become the object of considerable interest primarily due to theirsurprisingly high selectivity for paraffin dehydrocyclization to producearomatics under low pressure reforming conditions. However, it has alsobeen found that such catalysts are sensitive to certain types ofcontamination. Accordingly, there is an urgent need for a regenerationprocedure for these catalysts.

During reforming, conventional catalysts become deactivated by changesin the physical state of the catalytic metal and the accumulation ofcarbonaceous matter (such as coke) on the catalyst surface. Whendeactivation occurs, it is common practice to regenerate the catalyst.U.S. Pat. No. 3,496,096 granted on Feb. 17, 1970 to Kluksdahl, describesa catalyst regeneration procedure for a platinum/rhenium catalyst. Theprocedure involves three steps. In the first step the catalyst iscontacted with an oxygen containing gas at a temperature of less than800° F. which burns coke off the catalyst surface. In the second stepthe catalyst is again contacted with a gas containing oxygen and ahalide, but this time the temperature is between 800° F. and 900° F. Inthe final step the catalyst is contacted with a gas having a higheroxygen concentration and halide but at a temperature above 900° F. Theregenerated catalyst is then contacted with a gas containing hydrogen toreduce the valence states of the oxidized platinum and rhenium.Regeneration procedures such as thin one have become known in the art asoxychlorination procedures (see also U.S. Pat. No. 3,776,640 granted onDec. 4, 1973 to Moravec et al. which describes a similar procedure forremoving coke). One of their purposes is to redisperse platinumagglomerates which are formed during reforming or the coke burn.

U.S. Pat. No. 4,493,901 granted on Jan. 15, 1985 to Bernard et al.discloses a regeneration procedure for a coke deactivated zeolitereforming catalyst. Patentees use a hydration step following a coke burnand an oxychlorination step. The hydration step is carried out whilecontacting the catalyst with cool air after the oxychlorination step.Patentees add approximately 10 wt.% water to the cooling air.

European Patent Application No. 0 142 352 (Publication Number) filed onNov. 9, 1984 broadly describes a regeneration procedure for deactivatedL-zeolite catalysts. The deactivation addressed by the disclosedprocedure is caused by coke deposition and platinum agglomeration.Applicants employ a coke burn step and an oxychlorination step. However,when the redispersion procedures outlined in the European patentapplication are attempted on catalysts that have a binder, such assilica or alumina, the activity of the regenerated catalyst issubstantially lower than that of the fresh catalyst.

Sulfur may also cause catalyst deactivation. This is a particularproblem for large-pore zeolite catalysts having a Group VIII metal. SeeU.S. Pat. No. 4,456,527 granted June 26, 1984 to Buss et al.

Accordingly, there is still a need for a procedure which can restore theactivity of large-pore zeolitic catalysts having an inorganic binderwhich have been deactivated in whole or in part by the formation ofplatinum agglomerates. This need has now been satisfied by the inventionwhich is summarized and detailed below.

SUMMARY OF THE INVENTION

According to the present invention, a process is provided forredispersing platinum on a catalyst comprising L-zeolite and aninorganic oxide binder. The process comprises (a) oxychlorinating thecatalyst under oxychlorinating conditions; (b) contacting the catalystwith an inert gas; and (c) contacting the catalyst with dry hydrogen.The catalyst is preferably bound with clay, alumina, silica, orsilica-alumina. Preferably, the hydrogen stream contains less than 1000ppm water, more preferably less than 500 ppm water, most preferably lessthan 100 ppm water. It is also preferred that the inert gas is nitrogenand it preferably contacts the catalyst for a time between 10 minutesand 1 hour and 30 minutes.

The process more preferably comprises (a) contacting the catalyst underoxychlorinating conditions with a gas comprising 1% to 21% oxygen, 1% to4% water, and an effective amount of chlorine atoms to achieve achlorine to platinum ratio between 4:1 and 1000:1; (b) contacting thecatalyst with a gas comprising nitrogen, for a time between 10 minutesand 11/2 hours, at a gas flow rate of between 150 and 1500 GHSV, and ata temperature between 850° and 950° F.; and (c) contacting the catalystwith a gas comprising hydrogen having less than 1000 ppm water, at atemperature between 800° and 950° F. and a gas rate between 150 and 1500GHSV.

Among other factors, the process of the present invention is based on myfinding that a catalyst having a Group VIII metal, an inorganic oxidebinder, and L-zeolite can be regenerated to an unexpectedly highactivity by using relatively low severity conditions in the reductionstep of the process. Preferably, the lower severity conditions includethe use of relatively lower temperature in the reduction step than istypical in prior art processes and also the use of substantially dryhydrogen in this step. Additionally, I have found that higher activitycan be achieved if the inert gas purge time is limited in the process.

Gas flow rates are also an important element of the catalystregeneration process of the present invention. I have found that the gasflow rate in steps (a), (b) and (c) of the process should be maintainedat a relatively high level to attain regeneration of the catalyst tohigh activity. If the flow rate is diminished for step (a), (b) or (c),then the exposure time preferably is increased to attain the highactivity upon regeneration.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion presents a more detailed discussion of thepresent invention.

Monofunctional Large Pore Zeolite Catalysts

As explained in the Summary section, the present invention is aprocedure for regenerating large-pore zeolite catalysts. Hereinafter,the large-pore zeolite catalysts will simply be referred to as"catalysts". These catalysts generally comprise: a large-pore zeolite; aGroup VIII metal (such as noble metal, or more specifically, platinum);preferably the zeolite also contains a metal from either Group IA orIIA. Preferably, the large-pore zeolite is L-zeolite.

Large pore zeolites are defined as zeolites having an effective porediameter between 6 and 15 Angstroms. Among the large-pore zeolites whichhave been found to be useful in the practice of the present invention,type L zeolite, zeolite X, and zeolite Y are the most important and haveapparent pore sizes on the order of 7 to 9 Angstroms.

A composition of type L-zeolite, expressed in terms of model ratios ofoxides, may be represented as follows:

    (0.9-1.3)M.sub.2/n O:Al.sub.2 O.sub.3 (5.2-6.9)SiO.sub.2 :yH.sub.2 O

wherein M designates a cation, n represents the valence of M, and y maybe any value from 0 to 9. Zeolite L, its X-ray diffraction pattern, itsproperties, and method for its preparation are described in detail inU.S. Pat. No. 3,216,789 which is hereby incorporated by reference in itsentirety. The real formula may vary without changing the crystallinestructure; for example, the mole ratio of silicon to aluminum (Si/Al)may vary from 1.5 to 3.5.

The chemical formula for zeolite Y expressed in terms of mole oxides maybe written as:

    (0.7-1.1)Na.sub.2 O:Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O

wherein x is a value between 3 and 6, and y may be a value up to about9. Zeolite Y has a characteristic X-ray diffraction pattern which may beemployed with the above formula for identification. Zeolite Y isdescribed in more detail in U.S. Pat. No. 3,130,007. U.S. Pat. No.3,130,007 is hereby incorporated by reference in its entirety to show azeolite useful in the present invention.

Zeolite X is a synthetic crystalline zeolitic molecular sieve which maybe represented by the formula:

    (0.7-1.1)M.sub.2/n O:Al.sub.2 O.sub.3 :(2.0-3.0)SiO.sub.2 :yH.sub.2 O

wherein M represents a metal, particularly, alkali and alkaline earthmetals, n is the valence of M, and y may have any value up to about 8depending on the identity of M and the degree of hydration of thecrystalline zeolite. Zeolite X, its X-ray diffraction pattern, itsproperties, and method for its preparation are described in detail inU.S. Pat. No. 2,882,244. U.S. Pat. No. 2,882,244 is hereby incorporatedby reference in its entirety to show a zeolite useful in the presentinvention.

These zeolites contain exchangeable cations. Common cations that areuseful for catalysts of this invention are in Groups IA (alkali metals)and IIA (alkaline earth metals). When Group IA, alkali metals are used,sodium, potassium, lithium, rubidium, or cesium are preferred. WhenGroup IIA, alkaline earth metals are used, either barium, calcium, orstrontium is preferred. The alkaline earth metal can be incorporatedinto the zeolite by synthesis, impregnation or ion exchange.

In the present regeneration process it is important for the catalysts ofthis invention to contain one or more Group VIII metals, e.g.,ruthenium, rhodium, palladium, iridium, or platinum. The preferred GroupVIII metals are iridium, palladium, and particularly platinum. (Whenreference is made to a specific Group VIII metal, such as platinum, inthis application it is used as a representative of the group.) Thepreferred percentage of platinum, in the catalyst is between 0.1% and5%, the lower limit corresponding to minimum practical catalyst activityand the upper limit to roughly the maximum possible platinumutilization.

Group VIII metals are introduced into the large-pore zeolite duringsynthesis, impregnation or exchange in an aqueous solution of anappropriate salt. If it is desired to introduce two Group VIII metalsinto the large-pore zeolite, the operation may be carried outsimultaneously or sequentially.

By way of example, platinum can be introduced by impregnating thelarge-pore zeolite with an aqueous solution of tetrammineplatinum (II)nitrate [Pt(NH₃)₄ ](NO₃)₂, tetrammineplatinum (II) chloride [Pt(NH₃)₄]Cl₂, or dinitrodiamino-platinum [Pt(NH₃)₂ (NO₂)₂ ]. In an ionexchangeprocess, platinum can be introduced by using cationic platinum complexessuch as tetrammineplatinum (II) nitrate.

The presence of a binder is important in the present process. Aninorganic oxide is used as a matrix to bind the large-pore zeolite. Thisbinder can be a natural or a synthetically produced inorganic oxide orcombination of inorganic oxides. Typical inorganic oxide binders whichcan be used include clays, alumina, silica or mixtures thereof.Preferable binders are alumina, silica, or mixtures thereof. Acidicsites on the binder are preferably exchanged by cations which do notimpart strong acidity (such as sodium, potassium, rubidium, cesium,calcium, strontium, or barium).

After the desired metal or metals have been introduced, the catalystshould be calcined in air and then reduced in hydrogen. The catalyst mayhave a limited aqueous soak time and also be calcined in a steam-airmixture as specified in U.S. Pat. No. 4,608,356 granted Aug. 26, 1986 toBuss et al which is hereby incorporated by reference in its entirety. Atthis stage it is ready for use in the dehydrocyclization process.

The regeneration process of the present invention may be used oncatalysts in the form of extrusions, pills, pellets, granules, brokenfragments, or various other special shapes. The catalysts can becomedeactivated in any of the conventional types of equipment used forcatalytic reforming.

Sulfur and Coke Contamination

The present regeneration process is necessary due to platinumagglomeration which is a typical consequence of various types ofcontamination. For example, sulfur and coke contamination.

The sulfur sensitivity of these catalysts is known from U.S. Pat. No.4,456,527 to Buss et al which is hereby incorporated by reference in itsentirety. Sulfur contamination quickly lowers the catalytic activity forreforming reactions. To remove sulfur, various procedures have beendesigned, for example, see U.S. Ser. No. 944,403 which is herebyincorporated by reference in its entirety.

Coke can also contaminate and deactivate the catalyst and can begenerally described as an expected result of the reforming process.Hydrocarbons contact the catalyst and are dehydrogenated, some to theextent that only coke is left on the catalyst. As time increases, cokedeposition forces an adjustment of the process conditions to maintain acertain target octane number. However, there comes a time when theprocess conditions can no longer be adjusted to compensate for cokedeposition (much like sulfur contamination). It is at this point thatthe catalyst must be regenerated to restore its activity.

Sulfur and Coke Removal

Coke and sulfur removal processes are typically used prior to thepresent regeneration process. This removal preferably involves some typeof oxidation at least. When sulfur is removed in the fashion describedin U.S. Ser. No. 944,403, the platinum particles are intentionallyformed into large agglomerates. In this form, the catalyst is completelyinactive for reforming. Consequently, the platinum must be redispersedto restore the catalytic properties of the catalyst.

Likewise, when coke is removed from the catalyst by oxidation, platinumagglomerates are lilely to form if they are not already present as aresult of the reforming process itself. Typically, an oxidation step isused in advance of the basic oxychlorination process to burn coke offthe catalyst. A preferred example is as follows: The catalyst ispreferably contacted with a gas containing between 0.1 and 2.0 vol. %oxygen (for the purposes of this application gas concentrations areexpressed as a percent of the total volume). When more than 0.5% O₂ ispresent in the gas, care should be taken to minimize the catalysttemperature until the carbon level has been substantially reduced.Nitrogen or another inert gas is preferably present in a sufficientamount to make up the remainder of the gas. The temperature ispreferably between 500° F. and 800° F. The gas flow is preferablybetween 150 and 5000 GHSV, more preferably between 150 and 1500 GHSV.The pressure preferably ranges between 1 and 30 atmospheres, morepreferably between 1 and 10 atmospheres. Water is preferred in a rangebetween 0% and 10%. The catalyst is oxidized until sufficient coke hasbeen removed. The time can preferably range between 15 minutes and 10hours, more preferably between 30 minutes and 5 hours.

After coke or sulfur removal, the average size of the platinumagglomerates can range from 10 to 300 Angstroms (depending on theconditions used for removing the coke or sulfur). Platinum agglomeratesof this size must be redistributed over the catalyst to form particlessmaller than approximately 10 Angstroms. This is necessary if thecatalyst is to have an appreciable activity for aromatization.

Oxychlorination

The present regeneration process provides a method for redispersingGroup VIII metal agglomerates by an oxychlorination procedure.Basically, the oxychlorination procedure comprises contacting thecatalyst with an oxygen-containing gas and a chloride-containing gasfollowed by a nitrogen purge and a reduction. The procedure involvesthree steps.

In the first step the catalyst having platinum agglomerates is contactedwith a mixture of air, water, and chloride or chlorine atoms. Oxygen ispreferably present in a concentration of greater than 0.1%, morepreferably between 1% and 21% of the total gas volume. Water ispreferably present in a range of from 0.1% to 10%, more preferably from1% to 4%, and most preferably from 2% to 3%. The chloride or chlorineatoms are preferably present in an amount sufficient to achieve a ratioof chlorine to platinum atoms of between 4:1 and 1000:1, more preferablybetween 5:1 and 200:1, and most preferably between 10:1 and 50:1.Examples of possible chlorine or chloride compounds are: chlorine gas;organic chlorides, such as carbon tetrachloride (CCl₄); or hydrogenchloride (HCl). The temperature for the first step is preferably between800° F. and 1100° F., more preferably between 900° F. and 1000° F., andmost preferably between 925° F. and 975° F. The time for the first stepis preferably from 1 to 24 hours, more preferably 1 to 3 hours. Thespace velocity is preferably between 150 and 5000 GHSV, more preferablybetween 150 and 1500 GHSV. Pressure is preferably between 1 and 30atmospheres, more preferably between 1 and 10 atmospheres.

In the second step (also called a nitrogen purge) the catalyst ispreferably contacted with a dry inert gas, more preferably nitrogen, fora time sufficient to purge the catalyst bed of oxygen. "Dry" meanshaving preferably less than 1000 ppm water, more preferably less than500 ppm water, and most preferably less than 100 ppm water. Thisnitrogen purge step is preferably between 10 minutes and 11/2 hours,more preferably between 10 minutes and 1 hour. The temperature ispreferably between from 800° F. and 1000° F., more preferably between850° F. and 950° F., but most preferably between 875° F. and 925° F. Thegas velocities and pressures should be in the same ranges as the firststep.

In the third and final step (also called a hydrogen reduction step), thecatalyst is preferably contacted with dry hydrogen for a time sufficientto reduce all the exposed platinum. "Dry" means having preferably lessthan 1000 ppm water, more preferably less than 500 ppm water, and mostpreferably less than 100 ppm water. This time is dependent on thehydrogen flow and the reduction temperature. A shorter time is preferredbased on commercial considerations, for example, preferably less than 5hours, or more preferably between 1 and 4 hours. The temperatures ispreferably between 600° F. and 1000° F., more preferably between 800° F.and 950° F., and most preferably between 875° F. and 925° F. The gasvelocities and pressures are preferably in the same ranges as the firstand second steps.

An oxygen post-treatment step can be inserted between the first andsecond steps. In the oxygen posttreatment, the catalyst is preferablycontacted with an oxygen-containing gas having an oxygen concentrationgreater than 0.1%, more preferably between 1% and 21%. The temperatureis preferably between 800° F. and 1000° F., more preferably between 900°F. and 975° F. Water is preferably present in an amount between 0 and10%, more preferably between 1% and 4%, and most preferably between 2%and 3%. The gas velocities and pressures are preferably in the sameranges as the first, second and third steps.

It has been surprisingly found that in the final hydrogen reduction stepthe hydrogen should preferably have less than 1000 ppm water, morepreferably less than 500 ppm water, and most preferably, less than 100ppm water. Also, the amount of hydrogen preferably should be greaterthan 2 moles H₂ /mole platinum, more preferably greater than 10 moles H₂/mole platinum. Preferably, the hydrogen should have a total gasconcentration of between 1 vol. % and 100 vol. %, more preferably 10%and 100%, and most preferably 50% and 100%. If there is less than 1000%hydrogen, then an inert gas should preferably constitute the remainderof the gas.

The following examples are presented here as specific embodiments of theoverall concept of the present invention. They are intended to beexemplary and not restrictive in any way.

EXAMPLES EXAMPLE 1

The following example shows the regeneration of a sulfur contaminatedcatalyst according to the present invention. A catalyst comprising 0.8%platinum on a barium-potassium L-zeolite containing 8% barium wassulfided until it accumulated 317 ppm of sulfur and was substantiallydeactivated for paraffin dehydrocyclization [this is an isothermal testin which a light naphtha containing mostly C₆ -C₈ paraffins was reformedat 920° F., 100 psig and 6 liquid hourly space velocity]. Platinum atomson the surface of the catalyst were observed by transmission electronmicroscopy (TEM) and occurred in groups which are 10 to 20 Angstroms indiameter.

The deactivated catalyst was then subjected to a sulfur removal stepwhich is as follows. The catalyst was contacted with a gaseous stream of1% O₂ 99% N₂ at 900° F. and 250 GHSV for 24 hours. Then the catalyst wascontacted with a gaseous stream of carbon monoxide which had beenbubbled through a 32% HCl solution to give 3.5% HCl, 1% H₂ O, 95.5% CO.This operation was conducted at 900° F. and 250 GHSV, for 24 hours. Thesulfur concentration of the catalyst after treatment was 80 ppm.Platinum agglomerates, in the form of cubic crystals about 30 to 80Angstroms in the edge length, were observed on the catalyst by TEM. Thecatalyst was completely inactive for reforming reactions, includingcyclohexane dehydrogenation.

To restore activity to the catalyst, it was subjected to anoxychlorination step. This process was conducted as follows. Thecatalyst was contacted with wet air, at a flow rate of 1440 GHSV, and atemperature of 1000° F. for 1 hour. The wet air in this and laterexamples contained approximately 2% H₂ O and was obtained by saturatingair with water at room temperature. The pressure for this, and allfurther examples (unless noted), was 1 atmosphere. Then the catalyst wascontacted with a gaseous mixture of wet air at 1440 GHSV and atemperature of 900° F. for 2 hours, while chloride was injected ascarbon tetrachloride (CCl₄) at a ratio of approximately 20 chlorineatoms per 1 platinum atom. Thereafter, the wet air mixture was continuedat 1440 GHSV and 900° F. for an additional hour but without the CCl₄.Then, dry nitrogen was contacted with the catalyst at 1440 GHSV and 900°F. for 10 minutes. Following that, dry hydrogen was contacted with thecatalyst at 1440 GHSV and a temperature of 900° F. for 1 hour. Afterthis procedure, the catalyst was analyzed by TEM and it was observedthat the only visible platinum was present in agglomerates of 10Angstroms or smaller. After 20 hours onstream the catalyst was thentested for paraffin dehydrocyclization and it was found to have about40% of the activity of the fresh catalyst also measured after 20 hoursonstream. (K regenerated catalyst/K fresh catalyst=0.40)(K=(selectivity) [1n (1-conversion)]).

EXAMPLE 2

The following example shows regeneration of a deactivated catalystaccording to the present invention. Fresh, bound catalyst comprising0.8% platinum on a barium-potassium L-zeolite containing 8% barium(metal concentrations are based on the weight of the zeolite, however,the catalyst was bound with 20% SiO₂ which changes the metalconcentration for the bound catalyst) was reduced in H₂ at 900° F. for 1hour, purged with N₂ and then heated in wet air for 1 hour at 1000° F.The resulting catalyst had a dehydrocyclization activity of K/K_(fresh)=0.20.

To restore the activity to the catalyst, it was subjected to thefollowing oxychlorination step. The catalyst was contacted with agaseous mixture of wet air at 1440 GHSV and a temperature of 950° F. for2 hours, while chlorine was injected as carbon tetrachloride (CCl₄), ata ratio so that there were 20 chlorine atoms per 1 platinum atom. Then,dry nitrogen was injected at 1440 GHSV and 900° F. for 1 hour. Followingthat, dry hydrogen was contacted with the catalyst at 1440 GHSV and atemperature of 900° F. for 1 hour. The catalyst was then tested forparaffin dehydrocyclization and it was found that the activity wasgreater than the fresh catalyst (both measurements were made after 20hours onstream) (K regenerated catalyst/K fresh catalyst=1.15)(K=(selectivity) [1n (1-conversion)]).

The catalysts in the following examples contained 0.8 wt. % platinum ona barium-potassium L-zeolite containing 8 wt. % barium, the weightpercent calculated based on L-zeolite without a binder. Bound catalystscontain 20 wt. % inorganic binder, which reduced the overall platinumweight percent to 0.64% and the overall barium weight percent to 6.4%.

EXAMPLE 3

The following example shows a basic oxychlorination process usingdifferent conditions to achieve good results. It is not a strict exampleof the present invention because the L-zeolite is not bound and wethydrogen is used.

Four fresh catalysts were taken and subjected to the followingdeactivation and regeneration conditions.

    ______________________________________                                        Experiment No.                                                                           216      234       238    242                                      ______________________________________                                        Fresh Catalyst                                                                           L-Zeolite 238; no binder.                                          Deactivation                                                                             All catalysts were reduced in hydrogen                             Procedure  at 900° F. for 1 hour. Then they were                                  oxidized in wet 1% O.sub.2 in the following                                   conditions:                                                                 1000° F.                                                                      1000° F.                                                                         1050° F.                                                                        1050° F.                                     for    for       for      for                                                 3 hrs  3 hrs.    16 hrs.  16 hrs.                                    Oxychlorination                                                                          All the catalysts were contacted with                              Procedure  wet (about 2% H.sub.2 O) 1% O.sub.2 and CCl.sub.4 (at                         a ratio of 20 Cl/Pt atom) at 950° F. and                               1440 GHSV for 2 hours.                                             O.sub.2 Post                                                                             All the catalysts were contacted with                              Treatment  wet (about 2% H.sub.2 O) 1% O.sub.2 at 950° F. for                     1 hour at 1440 GHSV.                                               N.sub.2 Purge                                                                            All the catalysts were contacted with                                         wet (about 2% H.sub.2 O) N.sub.2 at 950° F. for                        10 minutes at 1440 GHSV.                                           H.sub.2 Reduction                                                                        All the catalysts were reduced in wet                                         (about 2% H.sub.2 O) hydrogen at 950° F. and                           1440 GHSV for the following times:                                          1 hr.  2 hr.     2 hr.    2 hr.                                      Activity Test                                                                            The following conversions*.sup.1 and                                          selectivities*.sup.2 were noted for each                                      catalyst for 3 hrs. onstream/20 hrs.                                          onstream:                                                          Conversion:                                                                              78/69    79/71     77/69  78/69                                    Selectivity:                                                                             71/81    71/78     73/81  75/81                                    ______________________________________                                         *.sup.1 Conversion is defined as the fraction of the reactants that is        converted to either aromatics or compounds with fewer than 6 carbon atoms     *.sup.2 Selectivity is defined as the fraction of converted reactants tha     are converted to aromatics.                                              

EXAMPLE 4

The following catalysts were treated in a similar manner to those inExample 3, but these were deactivated by coke fouling. Again, it is nota strict example of the present process because the zeolite is not boundand wet hydrogen is used. However, it is useful to show that the processwill work on an unbound, coke contaminated catalyst.

    ______________________________________                                        Experiment No.                                                                            222             230                                               ______________________________________                                        Fresh Catalyst                                                                            L-Zeolite 238; no binder.                                         Deactivation                                                                              These catalysts were run in a pilot                               Procedure   plant under standard reforming                                                conditions until they were substan-                                           tially deactivated for paraffin                                               dehydrocyclization.                                               Coke Burn   Both catalysts were contacted with 1%                                         O.sub.2 at 600° F. for 1 hr., then at 780° F.                   for 5 hrs. in the following amounts of                                        H.sub.2 O:                                                                  About 2%      0%                                                    Oxychlorination                                                                           The catalysts were contacted with wet                             Procedure   1% O.sub.2 for 2 hrs. at 950° F., 1440 GHSV                            and CCl.sub.4 to achieve a 33:1 ratio of                                      Cl/Pt.                                                            O.sub.2 Post                                                                              The catalysts were contacted with wet                             Treatment   1% O.sub.2 for 1 hr. at 950° F. and 1440 GHSV.             N.sub.2 Purge                                                                             Wet (about 2% H.sub.2 O) N.sub.2 at 950° F. for                        10 min.                                                           H.sub.2 Reduction                                                                         Both catalysts were subjected to wet                                          (about 2%) hydrogen at 950° F. for 3 hrs.                  Activity Test                                                                 Conversion: 70/64           67/51                                             Selectivity:                                                                              76/80           71/76                                             ______________________________________                                    

EXAMPLE 5

This example shows that unacceptable results are obtained when wethydrogen is used in regenerating a coke contaminated, bound catalyst.The following catalysts were treated in a similar manner to those ofExample 4, however, a binder was used to hold the catalyst powdertogether.

    ______________________________________                                        Experiment No.                                                                           226           228                                                  ______________________________________                                        Fresh Catalyst                                                                           L-zeolite     L-zeolite                                                       114           382                                                  Binder     Al.sub.2 O.sub.3                                                                            SiO.sub.2                                            Deactivation                                                                             The catalysts were run in a pilot plant                            Procedure  under standard reforming conditions until                                     they were substantially deactivated for                                       paraffin dehydrocyclization.                                       Coke Burn  The catalysts were contacted with 1% O.sub.2                                  for 1 hr. then at 780° F. for 5 hrs., both                             without H.sub.2 O.                                                 Oxychlorination                                                                          The catalysts were contacted with wet                              Procedure  1% O.sub.2 for 2 hrs. at 950° F., 1440 GHSV and                        CCl.sub.4 to achieve a ratio of 20:1 Cl/Pt.                        O.sub.2 Post                                                                             The catalysts were contacted with wet                              Treatment  1% O.sub.2 for 1 hr at 950° F. at 1440 GHSV.                N.sub.2 Purge                                                                            Wet N.sub.2 at 950° F. and 1440 GHSV for:                            30 min.     10 min.                                                  H.sub.2 Reduction                                                                        The catalysts were contacted with wet                                         (about 2%) hydrogen at 950° F. for 3 hrs.                   Activity Test                                                                 Conversion:                                                                              53/39         52/39                                                Selectivity:                                                                             65/70         67/70                                                ______________________________________                                    

EXAMPLE 6

This example shows that good results are obtained when dry N₂ and dry H₂are used at lower temperatures on a bound catalyst.

    ______________________________________                                        Experiment No.                                                                           278           285                                                  ______________________________________                                        Fresh Catalyst                                                                           L-zeolite     L-zeolite                                                       430           382                                                  Binder     SiO.sub.2     SiO.sub.2                                            Deactivation                                                                             Catalyst was  Coke fouling as                                      Procedure  reduced in    Example 5.                                                      hydrogen for 1 hr.                                                            at 900° F. Then it                                                     was oxidized in                                                               dry air at 1000° F.                                                    for 3 hrs.                                                         Coke Burn  No.           Coke burn as                                                                  Example 5.                                           Oxychlorination                                                                          The catalyst was                                                                            The catalyst was                                     Procedure  contacted with                                                                              contacted with                                                  wet air at 950° F.                                                                   wet air at                                                      for 2 hrs., 1440                                                                            1000° F. for 1 hr.                                       GHSV, and enough                                                                            Then wet air at                                                 CCl.sub.4 to achieve a                                                                      950° F. for 2 hrs.                                       20:1 Cl/Pt ratio.                                                                           with CCl.sub.4 added to                                                       achieve 20:1 Cl/Pt.                                  O.sub.2 Post                                                                             The catalyst was                                                                            The catalyst was                                     Treatment  contacted with                                                                              contacted with wet                                              wet air at 950° F.                                                                   air at 950° F. for                                       for 1 hr.     1 hr.                                                N.sub.2 Purge                                                                            Dry N.sub.2 at 900° F. for 1 hr. and 1440 GHSV.             H.sub.2  Reduction                                                                       Dry H.sub.2 at 900° F. for 1 hr. and 1440 GHSV.             Activity Test                                                                 Conversion:                                                                              79/71         75/67                                                Selectivity:                                                                             82/88         81/87                                                ______________________________________                                    

EXAMPLE 7

This example shows the effect of treating the catalyst with dry N₂ forvarying times in the nitrogen purge step.

    ______________________________________                                        Experiment No.                                                                          319      314     318    322   323                                   ______________________________________                                        Fresh Catalyst                                                                          L-zeolite 382 L-zeolite 485                                         Binder    All catalysts had SiO.sub.2 as a binder.                            Deactivation                                                                            Coke fouling as                                                                             Catalyst was                                          Procedure Example 4.    reduced in H.sub.2                                                            1 hr., then                                                                   oxidized in wet                                                               air at 1000° F.                                                        for 1 hr.                                             Coke Burn Coke burn as  No.                                                             Example 4.                                                          Oxychlorination                                                                         319 and 314   318, 322, and 323 were                                Procedure catalysts were                                                                              contacted with wet air                                          contacted with                                                                              at 950° F. 1440 GHSV and                                 wet air at    CCl.sub.4 to achieve a ratio                                    1000° F. for 1 hr.                                                                   of 20:1 Cl/Pt atoms.                                            Then wet air at                                                               950° F. 1440 GHSV                                                      for 2 hrs. and                                                                CCl.sub.4 to achieve                                                          a ratio of 20:1                                                               Cl/Pt atoms.                                                        O.sub.2 Post                                                                            The catalyst were contacted with wet air                            Treatment at 950° F. for 1 hr. at 1440 GHSV.                           N.sub.2 Purge                                                                           All the catalysts were contacted with dry                                     N.sub.2 at 900° F. for the following time                              periods:                                                                    1 hr.  2 hrs.  6 hrs.   16 hrs.                                                                             30 min.                                 H.sub.2 Reduction                                                                       All the catalysts were contacted with dry                                     H.sub.2 at 900° F. for the following time                              periods:                                                                      1 hr.    4 hrs.  4 hrs. 4 hrs.                                                                              1 hr.                                 Activity Test                                                                 Conversion:                                                                             75/70    64/60   64/49  67/52 67/58                                 Selectivity:                                                                            82/88    85/89   81/87  83/89 83/89                                 ______________________________________                                    

EXAMPLE 8

These experiments show the effect of a variety of flow rates.

    ______________________________________                                        Experiment No.                                                                           285         292          287                                       ______________________________________                                        Fresh Catalyst                                                                           All catalysts were zeolite 382.                                    Binder     All catalysts used SiO.sub.2 binder.                               Deactivation                                                                             Coke fouling as in Example 4.                                      Procedure                                                                     Coke Burn  Coke burn as in Example 5.                                         Oxychlorination                                                                          The catalyst was                                                                            The catalysts were                                   Procedure  contacted with                                                                              contacted with wet air                                          wet air at    at 950° F. for 2 hrs.                                    1000° F. for 1 hr.                                                                   with CCl.sub.4 added to                                         Then wet air at                                                                             achieve a 20:1 Cl/Pt                                            950° F. for 2 hrs.                                                                   ratio; at the following                                         with CCl.sub.4 added                                                                        rates:                                                          to achieve a                                                                20:1 Cl/Pt                                                                              480 GHSV     140 GHSV                                                 ratio. A flow                                                                 rate of 1440                                                                  GHSV was used.                                                     O.sub.2 Post                                                                             The catalysts were contacted with wet air                          Treatment  at 950° F. for 1 hr., but:                                           1440 GHSV 480 GHSV     140 GHSV                                      N.sub.2 Purge                                                                            Dry N.sub.2 at 900° F. for 1 hr., but:                               1440 GHSV 480 GHSV     140 GHSV                                      H.sub. 2 Reduction                                                                       Dry H.sub.2 at 900° F. for 1 hr., but:                                 1440 GHSV   480 GHSV     140 GHSV                                  Activity Test                                                                 Conversion:                                                                              75/67       57/42        13/5                                      Selectivity:                                                                             81/87       71/82        45/35                                     ______________________________________                                    

EXAMPLE 9

These experiments show the effect of pressure.

    ______________________________________                                        Experiment No.                                                                             778           811                                                ______________________________________                                        Fresh Catalyst                                                                             L-zeolite     L-zeolite                                                       436           488                                                Binder       SiO.sub.2     SiO.sub.2                                                     These two catalysts were treated                                              identically to Exp. No. 285 in the:                                           Deactivation Procedure, Coke Burn, O.sub.2                                    Post Treatment, N.sub.2 purge, and H.sub.2                                    Reduction. However, Exp. No. 778 was                                          run at 0 psig and Exp. No. 811 was run                                        at 150 psig. Other changes are listed                                         below:                                                             Oxychlorination                                                                            See Exp. No. 285                                                                            See Exp. No. 292                                   Procedure    in Example 8. in Example 8, the                                                             Cl/Pt ratio was                                                               115 and the time                                                              was 20 hours.                                      Activity Test                                                                 Conversion:  70/60         14/0                                               Selectivity: 83/88         50/0                                               ______________________________________                                    

EXAMPLE 10

These experiments show a compensatory effect for a low flow rate.

    ______________________________________                                        Experiment No.                                                                           297           298                                                  ______________________________________                                        Fresh Catalyst                                                                           L-zeolite 382                                                      Binder     SiO.sub.2                                                                     Both catalysts were treated the same as                                       Exp. No. 285 in Example 8 for the:                                            Deactivation Procedure; Coke Burn;                                            Oxychlorination Procedure; and the                                            Hydrogen Reduction, but the flow rate was                                     480 GHSV. Other changes are listed as                                         follows:                                                           O.sub.2 Post                                                                             The catalyst were contacted with 1% O.sub.2                        Treatment  at 950° F. and 480 GHSV for:                                         3 hrs.      1 hr.                                                    N.sub.2 Purge                                                                            The catalyst was contacted with dry N.sub.2 at                                900° F. and 480 GHSV for:                                              1 hr.         3 hrs.                                               Activity Test                                                                 Conversion:                                                                              67/57         72/64                                                Selectivity:                                                                             79/86         79/86                                                ______________________________________                                    

Experiment Nos. 297, 298, and 292 in Example 8 show how the times can beextended to compensate for the effect of low gas flow rate.

The embodiments of this invention which are exemplified above areintended solely as illustrations of the invention. They should not beinterpreted as limiting the scope of the invention to just thosefeatures which are exemplified. As those familiar with this area ofresearch will appreciate there are numerous variations of the inventionas defined in the following claims which have not been exemplified butwhich will achieve equivalent results.

What is claimed is:
 1. A process for redispersing platinum on a catalystthat has been used for reforming hydrocarbons which comprises platinum,L-zeolite having alkali or alkaline earth metals, and an inorganicbinder, the process comprising:(a) contacting the catalyst underoxychlorination conditions with a gas comprising 1% to 21% oxygen, 1% to4% water, and an effective amount of chlorine atoms to achieve achlorine to platinum ratio between 4:1 to 1000:1; (b) contacting thecatalyst with a gas consisting essentially of nitrogen for a timebetween 10 minutes and 1 hour and 30 minutes, at a gas flow rate ofbetween 150 and 1500 GHSV and at a temperature between 850° F. and 950°F.; and (c) contacting the catalyst with a gas consisting essentially ofhydrogen having less than 1000 ppm water, at a temperature between 875°F. and 925° F., and a gas velocity between 150 and 1500 GHSV.
 2. Theprocess as recited in claim 1 wherein the gas consisting essentially ofhydrogen contains less than 500 ppm water.
 3. The process gas recited inclaim 1 wherein the nitrogen contact time is between 30 minutes and 1hour.
 4. The process as recited in claim 1 further comprising removingcarbon from the catalyst prior to the oxychlorination procedure.
 5. Theprocess as recited in claim 1 further comprising removing sulfur fromthe catalyst prior to the oxychlorination procedure.